Yes, most members of the phylum Mollusca possess an open circulatory system. In an open circulatory system, the blood, known as hemolymph, is not confined entirely within blood vessels. Instead, it flows freely through cavities called sinuses, allowing it to directly bathe the organs.
This system is typical for many mollusks, including snails, clams, and octopuses. However, there are exceptions; for instance, some cephalopods like squids and octopuses have a more complex closed circulatory system, which is more efficient and supports their active lifestyles.
In summary, while an open circulatory system is common in many mollusks, there are variations within the group that showcase the diversity of adaptations in response to different ecological niches.